Howdy,
I am new here. Bought a plasma two weeks ago, and continued shopping around for an HTIB.
I just picked up my HTIB (SONY DAV-FR10W) two days ago, and spent a couple hours hooking stuff up the same night. It has a nice attractive, shiny metal case, with low profile and a rather broad flat top, flat enough to tempt placing another device on top of it. But, it was immediately apparent that the whole receiver runs extremely hot, hence the large shiny metal surfaces to maximise heat dissipation.
I believe the 'experts' here will agree that SONY is one of the better, (not the best by any stretch of the imagination), but one of the better HTIB manufacturers, especially with their Dream Systems. Nevertheless, the system is pretty compact, with DVD multistack, tuner, AMP etc. built right into a single compact box.
Electronic equipment generate heat as a consequence of the resistance losses when electricity flows through individual components. The more complex the device, the more components it is likely to have, and therefore, it is probably likely to generate more heat; not necessarily, but more likely than not (there are other factors such as quality, design, power, length of time on etc).
Electronic components have operating temp ranges that, when exceeded, components could fail. When the box is compact, devices are probably less spacious, and consequently, air flow may be more restricted, which means that cooling through the metal case, and specifically the large surface area on top and the bottom may become more important in cooling. When the device is low profile, and other (usually heat producing) components are stacked on top, one is left with a 'thermal' nightmare. Under those conditions, individual components inside the single box could fail.
In addition, when everything is in one box (tuner, CD/DVD player, amp etc), when one fails, the whole system is down. When you use components HT system, your DVD player fails, you toss it and replace for less than the cost of having a technician diagnose the problem as would be the case in an all-in-one system.
So, although I find that the average sales person at the Best Buy/Circuit City outlets are not particurlarly well informed, probably what ZEPHYR's friend at Best Buy was referring to was the components inside the box of an all-in-one system, as opposed to individual components of a true HT stacked system overheating, and he probably has a point there, though, in my research I never came across a reports of HTIBs having a (significant) disproportion of failure.
Having said all that, I personally preferred the HTIB vs stacked system, and was partial towards a SONY system to complement my 50" XBR plasma, though I may return it because it does not have a DVI to take full advantage of my HDTV's digital capabilities...
Bucky.